Inertia arming switch



Feb.. 3, i959 w. B. MCLEAN INERTIA ARMING SWITCH 2 Sheets-Sheet 1 FiledNov. 29, 1944 NVENTOR Feb. s, 1959 W .B MCLEAN 2,872,538

I INERTIA ARMING SWITCH Filed NOV. 29, 1944 2 Sheets-Sheet 2 l l l v yaATTORNEY INERTIA ARMIG SWITCH William B. McLean, Washington, D. C.,assignor to the United States of America as represented by the Secretaryf the Navy Application November 29, 1944, Serial No. 565,782 2 Claims.(Cl. 200 61.45) (Granted under Title 35, U. S. `Code (1952), sec. 266)This invention relates to arming switches of the type which is operatedby inertia and more particularly to a novel inertia arming switch foruse with explosive projectiles. The new switch operates upon sustainedacceleration of the projectile in flight to'close an arming circuit andupon substantial cessation of the acceleration to close a second armingcircuit whereby the switch provides a dual safety factor. The switch maybe used to particular advantage in electrically operated proximity fuzesfor rocket projectiles but may be used also with other types of fuzesand projectiles.

In tiring a projectile, such as a rocket with a proximity fuze or otherdetonating device employing an electronic tube, it is important for thesake of safety to delay the arming of the device until the projectilehas traveled a certain distance from the operator, and to a1- low timefor heating of the electronic tube. In this way premature explosionsresulting from the shock of tiring or from rough handling may beavoided.

An object of the invention is to provide a switch, operable by aset-back action or inertia, to close a circuit within a fraction of asecond after the elapse of a predetermined interval of time after ring.

Another object is to provide a switch which closes a second circuitafter a predetermined time interval subsequent to closing a rst circuit,after substantial cessation of the acceleration.

Another object is to provide a switch which operates only in response tothe sustained acceleration of a projectile and does not operate unlessboth the degree of acceleration and the duration thereof are suiiicient.The new switch resets to a safe position if the acceleration is notmaintained for a proper duration, and remains unresponsive to a suddenshock or to the cumulative elfect of repeated shocks.

A further object is in the provision of an additional safety feature inthe switch, comprising a movable shield covering the detonator during atime interval aft-er tiring.

Another object is to provide a setback switch for closing a plurality ofcircuits according to a predetermined time sequence and which is simplein construction and accurate in operation.

Other objects and advantages of the invention will appear in thefollowing speciiication, reference being had to the accompanyingdrawings in which Fig. l is a longitudinal section of a portion of aproximity fuze for an explosive projectile embodying one form of the newsetback switch, which is shown in elevation and in its set position;

Fig. 2 is a front elevation of the switch and its cylindrical housing;

Fig. 3 is a vertical section on the line 3 3 of Fig. l, the fuze canbeing omitted;

Fig. 4 is a plan view of the switch;

Figs. 5, 6 and 7 are vertical sections on the lines 5 5, 6 6 and 7 7,respectively, of Fig. 3;

Fig. S is a vertical section on the line 8 8 of Fig. 3,

372,53 Federated Feb. 3, 1959 particularly showing the relationship ofthe electrical contacts in the set position of the switch;

Fig. 9 is a side elevation of the switch as seen from the contact side,the switch again being shown in the set position;

Fig. l0 is a detail elevation of the switch from a position opposite tothat in Fig. 9, showing the position of the toothed wheel in response tosetback;

Fig. ll is a vertical section similar to Fig. 3 but omitting parts,showing the released position of the contacts as the result of thesetback action;

Fig. 12 is a .detail elevation of a portion of the switch shown in Fig.9, illustrating the closure of the electrical contacts when released bysetback;

Fig. 13 is a detail view partly in elevation and partly in section,Showing the final position of parts of the switch;

Fig. 14 is a perspective view of the toothed wheel,

showing the innermost structure; and

Fig. l5 is a fragmentary perspective view of the switch showing a safetykey for preventing insertion of the switch in a fuze assembly when theswitch is improperly set.

Reference is first made to Fig. 1 wherein 21 designates a portion of acan forming part of a proximity fuze for an explosive projectile, forexample, a fuze of the type disclosed in a copending application ofWilbur S. Hinman, Jr., and Harry Diamond, Serial No. 537,983, filed May30, 1943. The can is crimped or spun at 22 to hold a closure 23 in placeagainst a cup 24, the rim of which i's preferably welded or brazed tothe inside surface of the can. The cup contains a volume of tetryl 25'which constitutes the booster for the main powder charge in theprojectile (not shown).

An opening 25 centrally located in the bottom of thev cup 24communicates with a central opening 27 in a cover plate 2S which isscrewed into the internally threaded end 29 of a cylindrical housing 30for the setback switch 3l of my invention. The housing 3Q lits tightlybetween the plate 28 and the rim of a battery and condenser case 32. Apotting compound 33 immobilizes the cells of A, B and C batteries and acondenser (none shown). An end cap 3-4 is screwed into that end of thecase 32 adjacent the housing 30, for the purpose of confining thecompound 33 and providing a convenient means for mounting electricalconnections between the setback switch and the electrical apparatus inthe case 32.

The cap 34 has sockets 35, 36, 37, 38, 39 and 40 adapted to receiveplugs 4l, 42, 43, 44, 45 and 46, respectively, (Fig. 2) connected to thesetback switch 3l and to a detonator 47. The detonator is inserted in atube 4S located centrally of the switch chassis, where it is held inplace by the tension in the ends of a pair of clips 49, Sil. The clipsare included in a tiring circuit which, when closed, ignites thedetonator and thus the tetryl 25. The clips 49, 5@ are secured to aninsulating disk 51 which forms the forward face of the switch. A rivet52 secures the clip 49, while the clip 50 is secured by the plug 43.

The disk 51 is a rigid part of the switch chassis or case. It issuitably secured to a pair of plates 53, 54, as by means of partiallyswaged lugs 55 protruding from the forward edges of the plates throughopenings in the disk. The plates 53, 54 are spaced in parallelism by apair of partitions 56, 57 which are secured to the plates by partiallyswaged lugs. An insulating plate 58 is held between the plates 53, 54and carries exible contacts 59, 60 which, in the type of fuzecontemplated, serve to connect the detonator in a thyratron circuit whenthe contacts are bridged by a contacter 6l. The contacter 3 61 isembedded in an insulating slide 62 which does not move during-setbackcaused by acceleration of the projectile, but which does move afteracceleration has practically ceased, as will be described in greaterdetail presently.

The slide 62 occupies and is movable in a passageway formed by portionsof the plates 53, 54, the partitionv 57 and a portion of the cover plate20. The forward longitudinal ed es of the slide have racks 63 and 64,which, respectively, mesh with mutilated gears 65, 66 (Figs. 6 and 7) inthe initial or set position of he switch. 1n ,this position, a hole 67in the slide 62 is out of registration with the opening 27 and thecoaxial detonator tube 4S, the solid portions of the slide acting as asafety gate which guards the tetryl 25 from ignition should thed'etonator be fired prematurely.

Gear 65 has a suiciently long tooth course (Fig. 6) to insure drivingthe slide 62 laterally-of the switch to its final position (Fig. 13)wherein its hole 67 registers with the tube 48 to admit thel detonatorblast. The detonator is connected in circuit when the contacter 61bridges the contacts 59, 60, which occurs when the slide reaches its nalposition. The detonator circuit is thus closed and armed by the movingslide. Since some time is consumed by the gear 65 in driving the slide62 to its final or circuit-closing position, it follows that arming ofthe detonator circuit is delayed a definite time interval after theslide commences to move from its initial or set position.

Gear 66 has a'relatively short tooth course (Fig. 7), and the purpose ofthe few teeth initially in mesh with the rack 6d is to provide a directlocking of the sliding rack to the side frame by means of the pin. Tothis end, the gears 65, 66 turn as a unit since they are integral withthe ends of a connecting hub 60 between the plates 53, 54 (Fig. 3). Thehub and gear assembly is mounted upon and appropriately secured to ashaft 69 rotatably mounted in holes in the plates 53, 54. v

One end of the shaft 69 extends outwardly from the plate 53 and isannularly grooved to contain a spring key 70. The key 70 retains afreely rotatable toothed wheel 71 upon the shaft extension. The wheel 71has `a sleeve 72 (Fig. 3) around which a spring 73 is coiled, one end ofthe spring being anchored to a bracket 74 on the frame, and the otherend resting behind an off-centered weight 75 on the outer face of thewheel.

On the inner face of the wheel 71 is a hub 76 having a cam 77 formed byastep or cut-out portion. The hub has a marginal recess 78 (Fig. 14), theedges 78a, 73h ot which coincide with the ends of an arcuate slot 79 inthe toother wheel 71. This slot is adapted to be entered by the outerblunt end of a pin 80 during the setback action of the switch (Fig. 1l),but the pin S0 normally stands retracted from the slot and engages thecam 77 and its adjacent stop 77a in the set position of the switch (Fig.

l). The pin 80 is slidable axially in alined bores 31, 32 in portions ofthe gears 65, 66.

An arcuate slot 83 in the plate 53 receives a portion of the slidablepin 80, the extent of the slot 83 being approximately a half circle(Figs. and 13). A spring 84 tends to project the pin S0 into the slot79. For that purpose, the spring is carried by the pin (Figs. 3 and 11),its respective ends bearing against the gear 66 and a boss 85 on thepin. Preferably, the pin S0 extends throughran opening S7 in plate 54,and the adjacent end of the pin is reduced as shown at 86, to facilitateits withdrawal from opening S8 in the flange 89. The reduced end 86 otthe pin normally projects into an opening 30 in the flange S9 of asleeve 90 in the set position of the switch (Fig. 3).

rhe sleeve 90 is rotatably mounted on a stud 91 which is xed to the'plate 54. The rim of the flange 89'is recessed at 92 (Fig. 7) to receivea stop'93 which limitsV the extent of angular motion of the sleeve 90 byengagement of the stop with the ends of the recess. The stud 91 isheaded to retain the sleeve and is slotted to receive one end` of aspring 94 coiledaround they sleeve. The other end of the spring 94 ishooked onto an insulating quadrant 95, to the opposite sides of whichcontact segments 96, 97 are secured. These segments are engageable withcontacts 98, 99V and 100,101, respectively, which are paired off onopposite sides of an insulating supporting member 102'. The member 102is rigid because it is attached to posts secured to the plate 54, butthe quadrant 95 is movable because it is secured Vto the rotatablesleeve 90.

Contacts 98, 99 have attached wires of which 106, 107 may be regarded asbelonging to an A-battery circuit. Similarly, contacts 100,101 haveattached wires 108, 109 which may be regarded as belonging to aB-battery circuit, The respective circuits are closable-by the segments96, 97, upon release of the wheel 71 from its set position, thesubsequent engagement of contacts 59, 60 by the contactor 61'closing arelay circuit of which wires 110, 111 are to-be regardedas parts. i

The toothed Vrim of the wheel 71 is part of an escapement mechanismwhich slows the turning' of the wheel in either direction when releasedfrom its set position (Fig. 1). The rim coacts with pins 103 projectingfrom a utter weight 104 into the pathof the teeth at'equal distancesfrom a pivot 105 on which the weight is journaled. This serves to insurethat the switch will not be operated by shocks of short duration andalso provides delayed armingfafter cessation of acceleration.

The operationV of the device, briefly stated, comprises the clockwise.turning of the toothed wheel 71 (arrow a, Fig. 1) from its set position(Fig. l) in response to the inertia or setback of the weight 75 duringthe acceleration of the-projectile. The toothed wheel turns sufficientlyfar in the clockwise direction in approximately 0.08 second of timeafter the initiation of the setback action to cause the release of thequadrant 95 and the consequent closure of the A and B-battery circuits.When acceleration has practically ceased, the toothed wheel 71 is turnedin the opposite direction, that is, counter-clockwise (arrow b, Fig.10), Vby the spring 73 until it reaches its ultimateV position shown inFig. 13. Immediately upon starting on its counter-clockwise turn (Fig.10), the toothed wheel picks upv the pin which thereupon acts asA acoupling between the wheel and the gears 65,v 66, turning f the lattercounter-clockwise (arrow c, Fig. 13), and propelling the slideV 62 toits position of closing the plate circuit of a thyratron at the contacts59, 60. The delay-intime in closing the thyratron circuit by the slide62l-andf' its contactor 61 is a safety feature, since it minimizes theeffect of tarnsient voltages which appear across the thyratron gridcircuit during the warming up of the filamentsV of the radio tube in theA and B-battery circuits.

In amplifying the preceding description, the details of the operationare given as follows: The set position of the switch shown in Fig. 1 isobtained by pushing the pin 30 inwardly against the tension of thespring 84 (toV the right in Fig. 3) so'that its point 86 engages theopening 88 in the flange-89 and holds the quadrantr95 (Fig. 9) in thecircuit-opening position against the tension of the spring 94. Thesetting operationsy are done manually and require turning the wheel71'clockwise (in Fig. 1) as far as it will go, and turning the quadrantclockwise (in Fig. 9) as far as it will go.

When the device is rst assembled, the blunt end of the pin 80 projectsinto the slot 79 under pressure of the spring 84, thus loose-couplingthe pin and wheel 71. The relationship of the pin 80 and Wheel 71 toeach other at the start is as shown in Fig. 13, but the slide 62 is notnecessarily in the position there shown.

The quadrant 95 is turned to theposition in Fig..` 9 and;

distance of the arcuate slot 83, until the pin is stopped by the bottomextremity of slot 83.

The pin 80 is then in line with the hole 87, and the point 86 isinregistration with the opening 88. The wheel 71 is held while the pin80 is pushed endwise to engage the point 86 in the opening 88 (Fig. 3).The pushing is done with a pointed instrument inserted in the-slot 79(Fig. 1l) against the blunt end of the pin. As the operator releases thewheel 71, which tends to turn counter-clockwise (Fig. 1) by springpressure, he allows the pointed instrument to glide oi the blunt end ofpin Si) as the wheel advances, the pin Sti presently catching the cam 77(Fig. 3).

The clockwise turning of the wheel 71 which moves the pin 80 through theangle of 180 also moves the gears 65, 66 to the positions shown in Figs.6 and 7, placing slide 62 in its starting position (Figs. l, 3, 5, 6, 7and 9) upon the gears. The pin 80 remains at the bottom of the slot 83in the set position of the switch (Fig. 3), being held there byengagement of its reduced end portion in the hole 87. In this position,the blunt end of pin S6 rests upon cam 77. The wheel 71 is held in itsset position (Figs. l and 5) by engagement of the stop 77a with the pin80. The three electrical circuits are now open, the A-battery circuitbeing open at contacts 98, 99 (Fig. 9), the B-batte'ry circuit atcontacts 109, 101, and the relay circuit at contacts 59, 60.

Assuming that the projectile carrying the switch has been red, theinertia of the weight 75, which occupies a position below the axis ofWheel 71 (Fig. l), causes the wheel 71 to turn clockwise (arrow a, Fig.1). In other words, a setback action initially turns the toothed wheeluntil it reaches the approximate position in Fig. l0, where it remainsuntil acceleration of the projectile has practically ceased. While wheel71 is turning under the influence of setback, its-cam 77 drags acrossthe blunt end of the pin 80 until the pin is alined with the opening 78in the hub 76. Actuated by the spring 84, the pin is thereupon projectedthrough opening 78 and into the slot 79 and is withdrawn from openings87 and 88 (Fig. 1l).

The quadrant 95 is then released and, under the inuence of spring 94(Fig. 9), snaps into the circuit-clos ing position (Fig. 12). Thesegments 95 and 96 bridge the contact pairs 98, 99 and 100, 101,respectively, closing the A and B-battery circuits. After accelerationhas ceased, the counter-clockwise turning of wheel 71 (arrow b, Fig.under the inuence of spring 73, is impeded only by the escapementmechanism. As soon as the left end of the slot 79 (Fig. 10) catches upwith the pin 80, the pin and the gears 65, 66 are carried around in thecounter-clockwise direction (arrow c, Fig. 13) by spring 73, moving theslide 62 downwardly and nally bridging contacts 59, 60 with itscontactor 61. This closes the thyratron circuit including detonator 47.

Only sustained acceleration can move the weight 75 from the set positionof the switch (Fig. 1) to the required position (Fig. 10) to release theprimary switch 96-101. A sudden shock will not suice, due to thedelaying eiect of the escapement, nor can a succession of shocks becomeSuiiiciently cumulative to actuate the weight 75 to its trippingposition. The spring 73 will reengage the stop 77a with the pin 80 aftereach shock. Thus, the switch will not operate unless both the degree ofacceleration and duration of its application are sutiicient, and willreset to its initial position if the degree and duration of theacceleration are not suicient.

The closure of the A and B-battery circuits occurs during theacceleration of the projectile, but iinal arming is delayed a definiteinterval after the end of acceleration. This interval is governed by theescapement 71, 103, 104 and the strength of the spring 73. The rapiditywith which the slide 62 traverses the distance between its set andcircuit-closing positions (Figs. 1 and 13) determines the amount ofdelay in closing the thyratron-detonator 6 circuitl and in placing thedetonator 47 in communication with the tetryl 25 through the hole 67.

Referring to Fig. 15, 1 have shown a safety key 113 for preventing theslide 62 from arming completely and which locks the mechanism so thatthe key cannot be withdrawn unless the switches are in open circuitcondition. The

key has a lug 114 near one end, the lug being cut away to provide areduced portion 114a. A second lug 115 is disposed on the key inalignment with the lug 114 and separated from the reduced portion 114a`by a space substantially the width of the plate thickness 57. At itsopposite end, the key has a handle 116 which engages one end of a spring117 coiled around the key, the other end of the spring normally engagingthe disk 51 so as to urge the key outwardly from the switch. The key 113is inserted through key holes 11S in disk 51 and plate 56 and through akey hole 119 in plate 57, the hole 119 being similar to the holes 118except that it has an additional slot 119a somewhat smaller than the lug114.

The key 113 is inserted through the holes 118 and 119 and pressedagainst spring 117 until lug 114, 114a just clears the lower slot inhole 119. The key is then turned /until the lug 114 is aligned with theupper slot 119a,

whereupon the spring 117 moves the key outwardly to place the reducedlug portion 11451 in slot 119a, further outward movement of the keybeing prevented by the adjacent larger portion of lug 114. The key isnow in its locking position'wherein it lies in the path of movement ofslide 62 and prevents the slide from moving downwardly (Fig. l5) to itsarmed position. The slide 62 may be provided at its lower end with arecess 120 so that if the switch is accidently tripped, the movement ofthe slide is arrested by the key lug 114 entering the recess 120,whereby the key is held against rotation to its withdrawing position bythe walls of the recess 120. Thus, before the key can be withdrawn it isnecessary to reset the slide 62. The key handle 116 prevents the switchfrom being plugged into the fuze assembly as long as the key is in theswitch. However, when the slide 62 is properly set, the key 113 may bepushed inwardly to remove lug 114a from slot 11911 and then rotated andwithdrawn so as to permit insertion of the switch into the fuzeassembly.

The invention herein described may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

' I claim:

1. An inertia arming device comprising means rotatable in either of twodirections, said means having a recess, a spring-biased switch forclosing an electrical circuit, locking means to secure the switch in theopen-circuit position, a stop on said rotatable means spaced from therecess and holding the locking means in its locking position, a springacting to turn the rotatable means in one direction to maintain the stopin position against the locking means, an eccentric weight on saidrotatable means for causing reverse turning of the rotatable meansthrough the normal distance between the locking means and the recessagainst the tension of the spring during sustained acceleration, meansfor urging the locking means out of locking relation with the switch andinto said recess, a slide having a fixed stroke, racks disposed on twoparallel edges of said slidea pair of rotatable toothed gear-likemembers individually engaging said racks, said members initiallymaintaining said slide at one end of its stroke and upon turning of saidrotatable means in said one direction for effecting movement of saidslide to the other end of its stroke, and a iiutter weight having a pairof projections thereon in operative engagement with said rotatable meansfor eiecting a metered turning thereof in said one direction;

2. An inertia arming device comprising a switchoperating slide having aixed stroke, a rack on the slide,

aA gear engaging the rack and normally holding the'slide at one end ofits stroke, an actuating member movable b-y inertia, a switch elementbiased toward one position, latchingjmeans normally locking saidelementl in a second position and held in its locking position by theactuating member, said member being movable in one direction by inertiato release the latching means, a device operable upon release of thelatching means to move thelatching means for releasing the switchelement and coupling the gear to the actuating member, and meansoperable upon substantial termination of the inertia force to move theactuating member'in the oppositey direction and thereby move Vthe slidethrough said gear to the opposite end of its stroke.

References Cited in the file of this patent UNITED STATES PATENTS

